Imaging spectroscopy is widely used in remote sensing applications. One type of interferometric spectrometer used to supply spectral data for many remote sensing applications is called a Fourier Transform Spectrometer (FTS). A common form of an FTS employs a Michelson interferometer with one arm having a variable optical path length. The variable optical path length may be implemented using a movable minor. By scanning the movable mirror over some distance, an interference pattern or interferogram is produced at the imaging sensor (e.g., a focal plane array) that encodes the spectrum of the source (the amplitude of each incident spectral wavelength, or frequency, or wavenumber, is encoded as the amplitude of a cosine signal of given frequency). An FTS with a maximum optical path length difference (OPD) between the two arms of L centimeters (cm) provides a spectral resolution of 1/(2L) cm−1. The FTS uses the Discrete Fourier Transform (DFT) or its faster algorithm, the Fast Fourier Transform (FFT), to convert the auto-correlation to physical spectra. The encoded spectrum is the Fourier transform of the source. The FFT is efficient when large sample sets must be processed, but produces artifacts if the variable arm is not precisely controlled to provide uniformly spaced samples. The FTS also requires that the entire spectrum be computed at once, despite the fact that most spectral targets can be detected using only a few spectral samples or subsets of the spectrum. The DFT and FFT have limited spectral range due to aliasing effects, and once the band center is set in one part of the spectrum it cannot be modified elsewhere without recomputing the entire transform.
Commonly-owned U.S. Pat. No. 8,203,715 titled “KNOWLEDGE BASED SPECTROMETER,” which is herein incorporated by reference in its entirety, discloses an alternate configuration of an interferometric transform spectrometer that does not rely on DFT/FFT-based processing, and therefore can accommodate non-uniformly spaced samples. More specifically, U.S. Pat. No. 8,203,715 discloses a system in which the variable optical path length in one arm of the interferometer may introduce a maximum OPD of L (similar to the conventional FTS), but where knowledge of the “uncontrolled” sample step size and an alternative algorithm to the DFT/FFT is used to process the collected data.